Chapter 12ADO.NET

Yingcai Xiao

Introduction to Database

Computer Science: the science of data processing using a computational device.

Database (DB): a persistent store of data in a compact, secure, easy-and-fast-to-retrieve form.

Database Engine: a software program that creates and manages databases. (e.g. MS Jet Engine)

Database Management System (DBMS): a database engine plus user interfaces and other supporting software.

DBMS Examples: Oracle, DB2 (IBM), Sybase, Informix, Microsoft SQL Server, Microsoft Access, MySQL (public domain), …

Database Server: a DBMS that provides data to its remote clients.

.

Definitions

Definitions Cont. Database API: application programming interface to

DBMSs. Database Table: data are stored in a database as

“tables”. Each row of a table is called a record, each column of a table is called an attribute.

PhoneBook (Database Table Name)

Name Office Home Cell

Tom 330-972-5809 330-888-8888 330-168-8888

John 330-972-7777 330-777-7777 330-168-7777

… … … …

Database schema: meta data for databases, defining tables and their attributes.

SQL

SQL: Structured Query Language, a standardized language for accessing and manipulating

databases.

The Select-From-Where Clause:Select Office From PhoneBook Where Name=’Tom’;Select * From PhoneBook;

Three Parts of SQL: Query: data retrieval DML - Data Manipulation Language: inserting, deleting, updating, … DDL - Data Definition Language: table creation, alteration and drop.

SQL ExampleCREATE DATABASE pubs;USE pubs;CREATE TABLE authors( au_id varchar(11) NOT NULL, au_lname varchar(40) NOT NULL, au_fname varchar(20) NOT NULL, phone char(12) NOT NULL DEFAULT 'UNKNOWN', address varchar(40) NULL, city varchar(20) NULL, state char(2) NULL, zip char(5) NULL, contract bit NOT NULL, PRIMARY KEY(au_id));

SQL Example

insert authors values('409-56-7008', 'Bennet', 'Abraham', '415 658-9932', '6223 Bateman St.', 'Berkeley', 'CA', '94705', 1);

insert authors values('213-46-8915', 'Green', 'Marjorie', '415 986-7020', '309 63rd St. #411', 'Oakland', 'CA', '94618', 1);

DBMS Example: SQL Server

• By Microsoft• Needs runtime license• Best fit for .NET • Features

http://www.microsoft.com/sql/prodinfo/features/top30features.mspx

• Free version: SQL Server Expresshttp://www.microsoft.com/sql/editions/express/default.mspx

• Available in MSDNAA.

DBMS Example: MySQL

• By MySQL AB (part of Sun after 1/16/08)

• Free: http://dev.mysql.com/

• No need of runtime license

• Not the best fit for .NET

• Installed on all lab PCs.

• How to install it at home:http://www.cs.uakron.edu/~xiao/windows/MySQL-Installation.html

Database Programming

Architecture of a Three-Tier Application

DBMS / Database Server

Database

User Interface

Database Engine

Supporting Software

Application Server

Database API

Application Logic

App User InterfaceCLIENT

Architecture of a Three-Tier Application

Architecture of a Four-Tier Application

DBMS / Database Server

Database

User Interface

Database Engine

Supporting Software

Application Server

Database API

Application Logic

App User InterfaceWEB

SERVER

Architecture of a Four-Tier Application

WEB

CLIENT

ADO .NET ADO.NET is the database API for managed applications

(application servers) to talk to database servers (DBMS: Database Management Systems).

a database API for managed applications; a set of classes in .NET FCL System.Data namespace; designed to work over the Web; integrates effortlessly with XML; maps very well to stateless, text-based protocol HTTP; accesses databases through modules known as data

providers ( a set of APIs that make the accesses easy to program).

1. The SQL Server .NET provider interfaces to Microsoft SQL Server (7.0 or later) all managed code code runs faster code not portable to other databases

2. The OLE DB .NET provider OLE: Object Linking and Imbedding interfaces to databases through unmanaged OLE

DB providers: SQLOLEDB for SQL Server (6.5 or earlier), MSDAORA for Oracle and Microsoft, Jet.OLEDB.4.0 for Microsoft Jet database engine.

code runs slower code portable to other databases

Two Data Providers

The System.Data.SqlClient and System.Data.OleDb Namespaces

Classes in System.Data.SqlClient are for SQL Server .NET

using System.Data.SqlClient;

SqlConnection conn = new SqlConnection

("server=localhost;database=pubs;uid=sa;pwd=");

try { conn.Open ();

SqlCommand cmd = new SqlCommand ("select * from titles", conn);

SqlDataReader reader = cmd.ExecuteReader ();

while (reader.Read ()) Console.WriteLine (reader["title"]);

} catch (SqlException ex) {

Console.WriteLine (ex.Message);

} finally { conn.Close (); }

The System.Data.SqlClient and System.Data.OleDb Namespaces

Classes in System.Data.OleDb are for OLE DB .NET

using System.Data.OleDb;

OleDbConnection conn = new OleDbConnection("provider=sqloledb;server=localhost;database=pubs;uid=sa;pwd=");

try { conn.Open ();

OleDbCommand cmd =

new OleDbCommand ("select * from titles", conn);

OleDbDataReader reader = cmd.ExecuteReader ();

while (reader.Read ()) Console.WriteLine (reader["title"]);

} catch (OleDbException ex) {

Console.WriteLine (ex.Message);

} finally { conn.Close (); }

Pattern of database programming Create a connection object. Open the connection. Create a command object. Execute the command. Access the data. Close the connection.

Connections, Commands, and DataReaders Connection objects represent physical connections to a

database.SqlConnection or OleDbConnection

Command objects represent the commands performed on a database. SqlCommand or OleDbCommand

DataReader objects represent the data obtained by the commands.SqlDataReader or OleDbDataReader

Connection Objects The SqlConnection ClassThe ConnectionString

SqlConnection conn = new SqlConnection ();conn.ConnectionString =

"server=localhost;database=pubs;uid=sa;pwd=";orSqlConnection conn = new SqlConnection ("server=localhost;database=pubs;uid=sa;pwd=");

Errors in the connection string only throws exceptions at runtime.

ServerServerServer=localhost or Server=(local) or Data Source=(local)

SQL Server permits different instances of servers to be installed on a given machine.

server=DBSERVER (an database server computer named “DBSERVER” at the CS department of UA)

server=hawkeye\wintellect (an instance of SQL Server named Wintellect on a remote machine named Hawkeye)

Database or Initial Catalog: database name (e.g. Pubs)UID or User ID, Pwd: tempdb, tempdb

Min Pool Size and Max Pool Size, the size of the connection pool (the defaults are 0 and 100)

Integrated Security: default to false, otherwise uses Windows access tokens for authentication.

Connect Timeout: how many seconds to wait for a connection to open (default=15).

SqlConnection conn = new SqlConnection    

("server=hawkeye\wintellect;database=pubs;uid=sa;pwd=;" +   

"min pool size=10;max pool size=50;connect timeout=10");

Server

Exceptions and Closing Open Connections

Exceptions should never go uncaught, and open connections should always be closed before terminating. (Calling Close on a connection that’s not open isn’t harmful.)

SqlConnection conn = new SqlConnection

("server=localhost;database=pubs;uid=sa;pwd="); //before try block

try {conn.Open ();

// TODO: Use the connection

}

catch (SqlException e) {

Console.WriteLine (e.Message);

// TODO: Handle the exception

}

finally { conn.Close ();}

Command Classes: SqlCommand and OleDbCommand. – Encapsulate SQL commands performed on a

database.– Rely on connections established.– Include methods to execute the commands

encapsulated inside.

Example, delete a record from the Pubs database’s “Titles” table using an SQL DELETE command:

SqlCommand  cmd = new SqlCommand        ("delete from titles where title_id = 'BU1032'", conn);    cmd.CommandTimeout = 10; // Allow 10 seconds, default

30.cmd.ExecuteNonQuery (); // Execute the command

The ExecuteNonQuery Method For executing DML and DDL commands: CREATE, INSERT,

UPDATE, DELETE, … Not getting any data back. Examples:

SqlCommand cmd = new SqlCommand ("create database MyDatabase", conn);

cmd.ExecuteNonQuery ();

SqlCommand cmd = new SqlCommand ("create table titles …", conn); cmd.ExecuteNonQuery ();

SqlCommand cmd = new SqlCommand ("insert into titles (title_id, title, type, pubdate) " + "values ('JP1001', 'Programming Microsoft .NET', " + "'business', 'May 2002')", conn); cmd.ExecuteNonQuery ();

The ExecuteNonQuery Method SqlCommand cmd = new SqlCommand ("update titles set title_id = 'JP2002' " + "where title_id = 'JP1001'", conn); cmd.ExecuteNonQuery ();

SqlCommand cmd = new SqlCommand ("delete from titles where title_id = 'JP2002'", conn); cmd.ExecuteNonQuery ();

The ExecuteScalar Method

Executes a query command and returns a single value in the result set, such as COUNT, AVG, MIN, MAX, and SUM.

SqlCommand cmd = new SqlCommand ("select min (price) from titles", conn); decimal amount = (decimal) cmd.ExecuteScalar (); Console.WriteLine ("ExecuteScalar returned {0:c}", amount);

The ExecuteScalar Method Another common use for ExecuteScalar is to retrieve

BLOBs (binary large objects) from databases. For example, retrieving an image from the “Logo” field of the

Pubs database’s “Pub_info” table and encapsulates it in a bitmap:

use System.IO;use System.Drawing;use System.Data.SqlClient; SqlCommand cmd = new SqlCommand ("select logo from pub_info where pub_id='0736'", conn); byte[] blob = (byte[]) cmd.ExecuteScalar (); stream.Write (blob, 0, blob.Length); Bitmap bitmap = new Bitmap (stream); stream.Close ();

Write a BLOB to a database.FileStream stream = new FileStream("Logo.jpg",

FileMode.Open);

byte[] blob = new byte[stream.Length];stream.Read (blob, 0, (int) stream.Length);stream.Close ();

SqlCommand cmd = new SqlCommand("insert into pub_info (pub_id, logo) values ('9937', @logo)",

conn);cmd.Parameters.Add ("@logo", blob);

cmd.ExecuteNonQuery ();

The ExecuteReader Method For performing database queries and obtain the results as

quickly and efficiently as possible. Returns a DataReader object. Pulls back only the data to be “Read” by the DataReader

not all records satisfying the query condition.

SqlCommand cmd = new SqlCommand ("select * from titles", conn); SqlDataReader reader = cmd.ExecuteReader (); while (reader.Read ()) Console.WriteLine (reader["title"]);

Each call to “Read” returns one row from the result set. It uses a property indexer to extract the value of the

record’s “title” field. Fields can be referenced by name or by numeric index (0-

based).

DataReader Reads data. Reads schema (meta data) . Stream-based access to the results of database

queries. Fast and efficient. Read-only and forward-only. Closing a DataReader: reader.Close( )

does NOT close the connection, only frees it for others to use.

D-E-F-E-N-S-I-V-E P-R-O-G-R-A-M-M-I-N-G.

DataSets Set-based Database Accesses capture an entire query in memory support backward and forward traversal edit data and propagate the changes back to the

database.

DataSet, DataTable and DataAdapter .NET supports set-based database accesses

through three classes:

DataSet: equivalent of an in-memory database. It consists of a collection of DataTables.

DataTables are created by a DataAdapter (SqlDataAdapter and OleDbDataAdapter).

DataSet doesn’t interact with databases directly. DataAdapter reads the physical data sources and fills DataTables and DataSets

DataSets vs. DataReaders To simply query a database and read through the records

one at a time until you find the one you’re looking for, then DataReader is the right tool. DataReaders (1) retrieve only the data that you actually use, and (2) they don’t consume memory by storing every record that you read, but (3) but they can’t iterate backward.

To use all the query results and to iterate backward and forward through a result set, or to cache the result set in memory, use a DataSet.

Many controls that support DataSets are perfectly capable of binding to DataReaders.

DataGrid (GUI)

• DataGrid is an ASP control for displaying datasets.

• Database displaying procedure:– Use DataAdapter to get data from the

database.– Fill the data into a DataSet– Bind the DataSet to a DataGrid– Select the fields (columns) to be displayed and

their header texts.

Example: DataAdapter, DataSet and DataGrid (GUI)

<asp:DataGrid ID="MyDataGrid" OnItemCommand="OnItemCommand" RunAt="server"> <Columns> <asp:BoundColumn HeaderText="Title" DataField="title" /> <asp:BoundColumn HeaderText="Price" DataField="price" DataFormatString="{0:c}"/> <asp:ButtonColumn HeaderText="Action"

Text="Add to Cart" CommandName="AddToCart" /> </Columns></asp:DataGrid>

Examples/C9/Congo-Lab-MySQL/ViewCart.aspx

Example: DataAdapter, DataSet and DataGrid (GUI)

void Page_Load (Object sender, EventArgs e) { if (!IsPostBack) { string ConnectString = ConfigurationSettings.AppSettings["connectString"]; MySqlDataAdapter adapter = new MySqlDataAdapter ("select * from titles where price != 0", ConnectString); DataSet ds = new DataSet (); adapter.Fill (ds); MyDataGrid.DataSource = ds; MyDataGrid.DataBind ();//Bind data to GUI } }

Transaction Commands A transaction is a logical unit of operations grouped

together.

If one of the operations fails, the others will fail (or be rolled back).

Distributed transactions — transactions that span two or more databases.

The .NET Framework supports distributed transactions.

The .NET supports local transactions (one database):

Transacted Commands// Start a local transaction trans = conn.BeginTransaction (IsolationLevel.Serializable); // Create and initialize a SqlCommand object SqlCommand cmd = new SqlCommand (); cmd.Connection = conn; cmd.Transaction = trans; // Debit $1,000 from account 1111 cmd.CommandText = "update accounts set balance = " + "balance - 1000 where account_id = '1111'"; cmd.ExecuteNonQuery (); // Credit $1,000 to account 2222 cmd.CommandText = "update accounts set balance = " + "balance + 1000 where account_id = '2222'"; cmd.ExecuteNonQuery (); // Commit the transaction (commit changes) trans.Commit ();

Transacted Commands IsolationLevel.Serializable locks down the records while

they’re updated so that they can’t be read or written.

Committing the transaction writes the changes to the database.

Uses DataGrid to represent a DataSet in XML

DataSet ds = new DataSet ();

ds.ReadXml (Server.MapPath ("Bonuses.xml"));

MyDataGrid.DataSource = ds;

Summary

Database Programming: part of the architecture of a multi-tier application.

DB Programming API

ADO.NET

Data Providers (SQLServer Provider, OLEDB Provider)

Connection

Commands (NonQuery, Scaler)

DataReader

DataSet

DataAdapter

DataGrid

Transaction